It would help - greatly - if you were able to specify further. On what types of fights? Or are you simply looking for a stand-still-and-simlpy-dps scenario (usually called patchwerk)? 25M or 10M?

To give a non-specific answer to a non-specific question, I would say this: Elemental Shamans rarely do better dps than warlocks, while Balance Druids (if they know what they're doing) quite often beat us.

Funniest, as most enjoyable to play? I've only played elemental shaman and warlock out of the two, and warlock wins by a mile compared to elemental shamans. They have one of the most mind numbing rotations in game :P

If you like managing a pet, being occasionally needed for utility, and bringing DI and healthstones to the raid, play a warlock. As for 'fun', that's a purely personal decision. Try out all 3 and see what works for you.